220 EVENINGS AT THE MICEOSCOPE. 



dent of the circulation, there is a singular fusiform 

 vessel in the latter segments of the abdomen penetrat- 

 ing the tail-plate, on the ventral side. This vessel, now 

 and then, at irregular intervals, dilates quickly and 

 closes ; the wave proceeding upward toward the head, 

 but only for a short distance, and unattended with any 

 impulse to the blood-globules. The nature of this 

 vessel, and its use in the economy of the infant Crab, 1 

 can in no wise explain. 



